Pyrotechnic delays are used to control the time of events from the initiation of an initial impulse to the initiation of a secondary impulse, or output. Typically the delay is initiated by a thermal energy input. Timing is achieved by the linear reaction rate of a column of the pyrotechnic. Factors such as type of pyrotechnic ingredients, geometry of the pyrotechnic column, type and geometry of column of the pyrotechnic container, operation pressure and temperature are the parameters used in designing a pyrotechnic column. When the delay burns the desired length it intiates a secondary change which is the desired event. When the secondary event occurs the housing containing the pyrotechnic has no further need, and it either remains dormant or is destroyed. The device of the present invention allows a controlled use of the pyrotechnic delay column and housing while maintaining a controlled function of the timing event.
When a rocket is fired from the shoulder of a soldier, the delay time is necessary so the rocket will be at a safe distance from the gunner if the hot gases are expended after launch. The controlled hot gas expulsion provides additional impulse to the rocket.
The difference between this invention and other pyrotechnic delay devices is that the pyrotechnic delay device column housing is used as a bleed orifice for high pressure hot gases. The construction of this housing is such that the delay pyrotechnic is pressed such that a major portion of the pyro is mechanically supported which allows high pressure to be on the upper side of the delay column without extruding it through the vent orifices. At the lower outer edge is a transitional zone which has structure support in the direction of the external force. Once the delay pyro has burned into the transitional zone the external pressure then breaks thru and allows gas flow thru the column housing. This construction allows more precise control of the delay by supporting the pyro column thereby prohibiting premature break-up. This type of support differs from others in that there are no other supports below the delay column, and when the delay is complete, venting occurs through the delay housing to the atmosphere.
In one application, the delay mechanism is mounted in a rocket motor. The pyrotechnic delay device is mounted in a piston, which is mounted in the casing of a rocket motor. On the upper side of the piston is a solid propellant rocket motor and on the lower or aft side of the piston is a liquid held in the casing by a closure member. Responsive to ignition of the gas generator the piston is moved rearwardly, the closure member is ruptured and liquid is extruded through the nozzle by rearward motion of the piston. The liquid is expelled behind the gunner (the weapon is fired from the shoulder) and the missile is at a safe distance from the gunner when gases are expelled.